Doors of safes, vaults, strong rooms, and like security closures (hereinafter collectively referred to as safes) are provided with at least one and preferably a plurality of bolts that are reciprocated from a non-locking position to an extended locking position. When more than one bolt is provided, a boltwork comprising a group of links, cranks, and the like connect all bolts so that they may each be simultaneously moved when a single handle or wheel on the outside of the door is operated to extend the bolts to look the door or to withdraw the bolts to permit opening of the door. A locking device, usually a combination lock is also provided to secure the bolts in their extended locking positions. The lock contains its own bolt that will block or interfere with some part of the boltwork and prevent movement thereof and withdrawal of the bolts from their extended locking positions until such time as the combination lock is actuated to withdraw its bolt from its blocking position.
Burglars can, of course, attack locked safes by manipulating the combination lock until the correct combination is found, at which time the safe can be opened as with any authorized opening of the safe. Or a hole can be drilled through the safe door to enable a burglar to view the interior mechanism of the lock and line up the combination disks so that the lock bolt can be withdrawn in the usual way. However, the usual method is to physically or mechanically attack the combination lock as by punching, drilling, or burning the lock to gain access to the lock bolt and permit its movement out of its locking position. When it is so moved, the safe handle or wheel is operated to withdraw the bolts from their extended locking positions and thereby permit opening of the safe door.
To foil such efforts to crack a safe, a drill resistant hardplate may be provided under the combination lock or, in rare instances, around the lock. However, given the right tools and enough time, a skilled burglar can penetrate the hardplate and defeat its function of protecting the lock.
Also known in the art are relocking devices that embody an additional bolt that blocks some part of the boltwork and prevents operation of the safe handle or wheel to withdraw the locking bolts from their locking position. Such an additional bolt is normally held out of its blocking position but is spring biased to move into a blocking position when the safe combination lock is under attack. The mechanism for triggering operation of the relocking device bolt may be a movable plate that is moved when an attempt is made to punch, drill, or otherwise attack the combination lock. Or it may be a fragile glass plate mounted beneath the combination lock that will shatter when subjected to attack thereby freeing the relocking mechanism bolt to be biased to its relocking position. Both such relocking mechanisms are disclosed in U.S. Pat. No. 4,266,488. Other arrangements such as blocking the combination lock bolt when the lock is under attack are disclosed, for example, in U.S. Pat. No. 4,147,044.
All relocking mechanisms known to applicants are mechanical in nature as in the mentioned disclosures. As such they are designed for a particular safe and are incorporated therein when the safe is manufactured. They do not lend themselves for retrofitting to existing safes, nor do they lend themselves to a flexible or variable design for individual safes of a particular model of safe. Thus, burglars who are familiar with a particular model of safe will know exactly where, on that particular model of safe, the relocking bolt is located so it can be attacked as well as the primary combination lock bolt.